Twelve-strand rope employing jacketed sub-ropes

ABSTRACT

A rope structure is formed by forming a sub-rope structure comprising a core and a jacket, twisting the sub-rope structure to form a twisted sub-rope structure, and forming the rope structure by braiding together a plurality of lengths of the twisted sub-rope structure.

TECHNICAL FIELD

The present invention relates to rope structures, systems, and methods and, in particular, to such structures, systems, and methods in which a twelve-strand rope is formed by jacketed sub-ropes.

BACKGROUND

Rope structures are commonly used when a tension load is to be applied between two structures. One common use of a rope structure is as a mooring tether or line adapted to extend between a first structure (e.g., oil drilling or production platform or vessel) and a second structure (an anchor on the sea floor).

Mooring tethers or lines are commonly formed with a core for tensile strength and a jacket to cover and protect the core. The core in turn is formed by strands. The protective jacket prevents visual inspection of the load bearing core and/or the strands forming the load bearing, so it is difficult to determine whether the load bearing core of a jacketed mooring tether or line may be subject to failure.

The need thus exists for improved mooring lines that facilitate visual inspection of individual strands of a jacketed core.

SUMMARY

The present invention may be embodied as a method of forming a rope structure comprising the following steps. A sub-rope structure comprising a core and a jacket is formed. The sub-rope structure is twisted to form a twisted sub-rope structure. The rope structure is formed by braiding together a plurality of lengths of the twisted sub-rope structure.

The present invention may also be embodied as a rope structure comprising a plurality of lengths of a sub-rope structure comprising a core and a jacket. A reference line substantially parallel to a longitudinal axis of the sub-rope structure when the rope sub-structure is initially formed is substantially parallel to the longitudinal axis of the rope sub-structure when the plurality of lengths of the sub-rope structure are braided together to form the rope structure.

The present invention may be embodied as a method of forming a rope structure comprising the steps following steps. A rope sub-structure comprising a core and a jacket is provided. An amount of braid twist obtained when braiding the rope sub-structure to form the rope structure is determined. A twisted sub-rope structure is formed by pre-twisting the sub-rope structure to compensate for the braid twist. Lengths of the twisted sub-rope structure are braided together to form the rope structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating a first example step of a process of making a twelve-strand rope structure of the present invention;

FIG. 2 is a schematic block diagram illustrating a second example step of a process of making a twelve-strand rope structure of the present invention;

FIG. 3 is a schematic block diagram illustrating a third example step of a process of making a twelve-strand rope structure of the present invention;

FIG. 4 is a somewhat schematic section view of an example sub-rope produced by the third example step depicted in FIG. 3;

FIG. 5 is a schematic block diagram illustrating a fourth example step of a process of making a twelve-strand rope structure of the present invention;

FIG. 6 is a somewhat schematic plan view of an example sub-rope produced by the third example step depicted in FIG. 3;

FIG. 7 is a somewhat schematic plan view of an example twisted sub-rope produced by the fourth example step depicted in FIG. 5;

FIG. 8 is a schematic block diagram illustrating a fifth example step of a process of making a twelve-strand rope structure of the present invention;

FIG. 9 is a somewhat schematic depiction of an example twelve-strand rope of the present invention; and

FIG. 10 is a somewhat schematic section view of an example sub-rope produced by the third example step depicted in FIG. 3 but further comprising a filter member.

DETAILED DESCRIPTION

Referring to FIGS. 1-5 of the drawing, depicted therein are first, second, third, fourth, and fifth steps, respectively, of a method of fabricating a twelve-strand rope structure in accordance with, and embodying, the principles of the present invention. FIG. 6 schematically illustrates an example twelve-strand rope 20 manufactured using the systems and methods depicted in FIGS. 1-5.

Referring initially to FIG. 1 of the drawing, schematically depicted therein is a first or yarn forming step performed by a twisting system 30 comprising a creel system 32 and a first twister 34. The creel system 32 supports spools or bobbins 40 on which are stored filaments 42. The first twister 34 unspools the filaments 42 from the bobbins 40 and twists the filaments 42 together to obtain yarns 44 comprising a plurality of the filaments 42. The yarns 44 are taken up on yarn bobbins 46 for storage and subsequent processing as will be describe in further detail below. The creel system 32 and first twister 34 are or may be conventional and will not be described herein in further detail. The filaments 42 typically comprise one or more synthetic fibers, and the manufacture of the yarns 44 from the filaments 42 using the creel system 32 and first twister 34 also may be conventional.

Schematically depicted in FIG. 2 of the drawing is a second or sub-rope core forming step performed by a first braiding system 50 comprising a 12-strand braider system 52 and a plurality of the yarn bobbins 46 each containing a length of the yarn 44. The 12-strand braider system 52 is or may be conventional and will not be described herein in further detail. For simplicity, five yarn bobbins 46 are depicted in the schematic representation of the first braiding system 50 in FIG. 2, but it will be understood that twelve yarn bobbins 46 and twelve lengths of the yarn 44 are used by the 12-strand braider system 52 of the first braiding system 50. In particular, the 12-strand braider system 52 pulls the twelve lengths of yarn 44 and combines these lengths of yarn 44 to form a core structure 54 in the form of a twelve-strand braided rope. The core structure 54 is taken up on a core bobbin 56.

FIG. 3 of the drawing schematically depicts a third or sub-rope forming step performed by a second braiding system 60 comprising a cover braider system 62, a plurality of the yarn bobbins 46 each containing a length of the yarn 44, and one the core bobbins 56 containing a length of the core structure 54. The example cover braider system 62 is or may be conventional and will not be described herein in further detail. For simplicity, five yarn bobbins 46 are depicted in the schematic representation of the second braiding system 60 in FIG. 3, but it will be understood that twelve yarn bobbins 46 and twelve lengths of the yarns 44 are used by the cover braider system 62 of the second braiding system 60. In particular, the cover braider system 62 pulls the core structure 54 and the twelve yarns 44 and combines the core structure 54 and the pulled yarns 44 to form a sub-rope structure 64.

As perhaps best shown in FIG. 4 of the drawing, the example sub-rope structure 64 comprises a jacket structure 68 formed by the yarns 44 and a core formed by the core structure 54. The sub-rope structure 64 thus takes the form of a jacketed twelve-strand braided rope. The sub-rope structure 64 is taken up on a sub-rope bobbin 66.

FIG. 5 of the drawing schematically depicts a fourth or pre-twist forming step performed by a second twister system 70 comprising a second twister 72 and a sub-rope bobbin 68 comprising a length of the sub-rope structure 64. The second twister 72 unspools the length of sub-rope structure 64 from the sub-rope bobbin 68 and twists the sub-rope structure 64 to obtain a twisted sub-rope structure 74. The twisted sub-rope structure 74 is taken up on a twisted sub-rope bobbin 76 for storage and subsequent processing as will be describe in further detail below. The second twister 72 is or may be conventional and will not be described herein in further detail.

FIGS. 6 and 7 schematically represent the untwisted sub-rope structure 64 and the twisted sub-rope structure 74 obtained after the untwisted sub-rope structure 64 is processed by the second twister system 70. In particular, for reference purposes, a straight reference line 78, shown as a dashed line in FIG. 6, is defined along a length of the untwisted sub-rope structure 64 and parallel to the longitudinal axis of that structure 64. It should be apparent that the reference line 78 is not a feature of the sub-rope structure 64 but would be formed solely for the purpose of illustrating the difference between the untwisted sub-rope structure 64 and the twisted rope structure 74. After the pre-twist step is performed, the reference line 78 follows a helical path, as shown by dashed lines in FIG. 7, centered about the longitudinal axis of the twisted rope sub-structure 74. A similar convention of straight and angled (helical) dashed lines is used in FIG. 5 to distinguish between the un-twisted sub-rope structure 64 going into the second twister system 70 and the twisted sub-rope structure 74 leaving the second twister system 70.

FIG. 8 of the drawing schematically depicts a fifth or rope forming step performed by a third braiding system 80 comprising a 12-strand braider system 82 and a plurality of the twisted sub-rope bobbins 76 each containing a length of the twisted sub-rope structure 74. The example 12-strand braider system 92 is or may be conventional and will not be described herein in further detail. For simplicity, five sub-rope bobbins 76 are depicted in the schematic representation of the third braiding system 80 in FIG. 8, but it will be understood that twelve sub-rope bobbins 76 and twelve lengths of the twisted sub-rope structure 74 are used by the 12-strand braider system 82 of the third braiding system 80. In particular, the 12-strand braider system 82 pulls the twelve lengths of the twisted sub-rope structure 74 and combines these lengths of twisted sub-rope structure 74 to form the rope structure 20 comprising a plurality of assembled sub-rope structures 84. The rope structure 20 is taken up on a 12-strand rope bobbin 86 for subsequent storage and handling prior to use.

12-strand braiders such as the example 12-braider system 82 inherently form a twist in the sub-rope structures braided thereby. For many sub-rope structures, the twist is inconsequential. For jacketed sub-rope structures, the twist formed by the 12-strand braider deforms the jacketed sub-rope structure and thus the twelve-strand braided rope formed thereby. Accordingly, jacketed sub-rope structures are not effectively used to form a rope structure using 12-strand braiders.

The Applicants have discovered that the performance of the pre-twist step to twist sub-rope structure ultimately taken up by a conventional 12-strand braider can compensate for the twist applied by a 12-strand braider. In particular, the pre-twist step performed by the second twister system 70 is configured to yield a twisted sub-rope structure 74 having an amount of pre-twist in a first direction to compensate for an amount of braid twist applied in a direction opposite the first direction by the 12-strand braider system 82.

Accordingly, as shown in FIG. 8 and in more detail in FIG. 9, when the lengths of twisted sub-rope structure 74 are combined to form the assembled sub-rope structures 84 of the rope structure 20, the pre-twist in the twisted sub-rope structures 74 is removed by the braid twist as shown by the dashed reference lines 78 in FIG. 8. FIG. 8 further shows that, after the inherent twist of the 12-strand braider system 82 is applied to the twisted sub-rope structure 74, the reference lines 78 on the resulting assembled sub-rope structures 84 define are again substantially parallel to the longitudinal axis of the sub-rope structure 20.

Because the assembled sub-rope structures 84 are not twisted, these sub-rope structures 84 do not deform and/or result in deformation of the final rope structure 20. Further, the final rope structure 20 need not be jacketed to cover the assembled sub-rope structures 84 because the assembled sub-rope structures 84 are themselves jacketed. If the final rope structure 20 is used, as an example, as a mooring tether or line, the assembled sub-rope structures 84 are easily inspectable.

As shown in FIG. 10, the method of the present invention may further comprise the step of arranging a filter member 90 between the core structure 54 and the jacket structure 68 before or while the jacket structure 68 is being formed. The filter member 90 may be a long strip of filter paper wrapped in a helix around the core structure 54 or may be a long thin sheet of filter paper folded around the core structure 54. In either case, the filter member 90 inhibits egress of sediment and the like into the core structure 54.

The filaments 42 may be made of one or more fibers made of the following materials: Polyester, Polyethylene, Polypropylene, Nylon, Aramid, Liquid Crystal Polymer, copolymers, High Modulus Polyethylene, Glass, Carbon, and Basalt. 

What is claimed is:
 1. A method of forming a rope structure comprising the steps of: forming a sub-rope structure comprising a core and a jacket; twisting the sub-rope structure to form a twisted sub-rope structure; forming the rope structure by braiding together a plurality of lengths of the twisted sub-rope structure.
 2. A method as recited in claim 1, further comprising the steps of: forming strands from filaments; and combining lengths of the strands to form the core and the jacket of the sub-rope structure.
 3. A method as recited in claim 2, in which: the step of combining the strands to form the core comprises the step of braiding together twelve lengths of the strands; and the step of combining the strands to form the jacket comprises the step of braiding together twelve lengths of the strands around the core.
 4. A method as recited in claim 1, in which the step of twisting the sub-rope structure to form the twisted sub-rope structure further comprises the steps of: determining an amount of braid twist applied when the lengths of twisted sub-rope structures are braided together to form the rope structure; and applying sufficient pre-twist when forming the twisted sub-rope structure to compensate for the braid twist.
 5. A method as recited in claim 1, further comprising the step of arranging a filter member between the core and the jacket.
 6. A method as recited in claim 1, in which the step of forming the rope structure comprises the step of braiding together twelve of lengths of the twisted sub-rope structure.
 7. A rope structure comprising a plurality of lengths of a sub-rope structure comprising a core and a jacket, where a reference line substantially parallel to a longitudinal axis of the sub-rope structure when the rope sub-structure is initially formed is substantially parallel to the longitudinal axis of the rope sub-structure when the plurality of lengths of the sub-rope structure are braided together to form the rope structure.
 8. A rope structure as recited in claim 7, in which: lengths of strands are braided together to form the core and the jacket of the sub-rope structure; and the strands comprise filaments.
 9. A rope structure as recited in claim 8, in which: the core of the rope sub-structure comprises twelve lengths of the strands; and the jacket of the rope sub-structure comprises twelve lengths of the strands.
 10. A rope structure as recited in claim 8, further comprising a filter member between the core and the jacket.
 11. A rope structure as recited in claim 8, in which the rope structure comprises twelve of lengths of the sub-rope structure.
 12. A method of forming a rope structure comprising the steps of: providing a rope sub-structure comprising a core and a jacket; determining an amount of braid twist obtained when braiding the rope sub-structure to form the rope structure; and forming a twisted sub-rope structure by pre-twisting the sub-rope structure to compensate for the braid twist; braiding lengths of the twisted sub-rope structure together to form the rope structure.
 13. A method as recited in claim 12, further comprising the steps of: forming strands from filaments; and combining lengths of the strands to form the core and the jacket of the sub-rope structure.
 14. A method as recited in claim 13, in which: the step of combining the strands to form the core comprises the step of braiding together twelve lengths of the strands; and the step of combining the strands to form the jacket comprises the step of braiding together twelve lengths of the strands around the core.
 15. A method as recited in claim 13, further comprising the step of arranging a filter member between the core and the jacket.
 16. A method as recited in claim 13, in which the step of forming the rope structure comprises the step of braiding together twelve of lengths of the twisted sub-rope structure. 